1. Field of the Invention
This invention relates to a phase difference element typified by a half or quarter wave plate. More particularly, it relates to a phase difference element exploiting the difference in the refraction index in the planer axial direction in a light bandwidth in use, and a method for manufacturing the same.
2. Description of Related Art
Conventionally, the phase difference element is manufactured from an inorganic optical single crystal, such as quartz, or from a stretched high molecular film. The inorganic optical single crystal, while being satisfactory in performance, durability and reliability as phase difference element, suffers the problem that the cost of raw materials and the processing cost are high and that the optical characteristic of the phase difference element exhibits marked incident angle dependency. The stretched high molecular film, a most popular phase difference element in current use, has a drawback that it may readily be deteriorated against heat or UV light rays and hence is problematical in durability.
On the other hand, there is known, as such phase difference element, an obliquely vapor deposited film having an oblique or inclined columnar structure (obliquely vapor deposited phase difference element). See for example Patent Publications 1 to 3 and Non-Patent Publication 1. As a principle, it is possible with this obliquely vapor deposited film to set a desired phase difference value by adjusting the film thickness and to increase its surface area with relative ease as well as to reduce the cost by volume production. In addition, since the phase difference element is formed of an inorganic material, it is highly resistive against light and heat.